Convert PNG image to grayscale without losing transparency using Delphi

I want to convert a PNG image to grayscale with transparency (not losing alpha channel). Probably using TBitmap and TPngImage components or Skia4Delphi.

From to

But how? I'm using Delphi 10.3.3 VCL.

Using Skia4Delphi library:

uses
  System.UITypes, Skia;

procedure TForm1.FormCreate(Sender: TObject);
var
  LImage: ISkImage;
  LSurface: ISkSurface;
  LPaint: ISkPaint;
begin
  LImage := TSkImage.MakeFromEncodedFile('..\..\delphi.png');
  LPaint := TSkPaint.Create;
  LPaint.ColorFilter := TSkColorFilter.MakeHighContrast(TSkHighContrastConfig.Create(True, TSkContrastInvertStyle.NoInvert, 0));
  LSurface := TSkSurface.MakeRaster(LImage.Width, LImage.Height);
  LSurface.Canvas.Clear(TAlphaColors.Null);
  LSurface.Canvas.DrawImage(LImage, 0, 0, LPaint);
  LSurface.MakeImageSnapshot.EncodeToFile('..\..\delphi-grayscale.png');
end;